Patent GB-1071576-A (GB)
Title: Improvements in and relating to methods of manufacturing semiconductor devices
IPC: H01L21/34
Filed: 1964-06-17
Abstract: 1,071,576. Semi-conductor devices. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. June 17, 1964 [June 20, 1963], No. 25071/64. Heading H1K. In a Thin Film Transistor (TFT) comprising a semi-conductor layer on a carrier, source and drain electrodes forming a first electrode pattern, and a gate electrode, which is located on the semi-conductor layer between the source and drain electrodes, forming a second electrode pattern, one of the electrode patterns is first formed and subsequently the other electrode pattern is formed using a photographic process with the aid of an optical image of the first formed pattern, so that when viewed normally to the semi-conductor layer at least parts of the two electrode patterns are substantially complementary and non-overlapping. As shown, Figs. 1 and 3, the source and drain electrodes 2, 3 of a TFT are produced on a glass substrate 1 by vapour deposition of silver through a mask or using a photolithographic technique. A thin layer 5 of N-type SnO 2  is vapour deposited over the electrodes and an insulating layer 6 of silicon oxide is deposited on top of it. Layer 6 may cover the whole of layer 5 or may be limited to the central portion. A thin film 7 of gold is vapour deposited on the oxide layer 6 in the shape of a transverse strip and is covered with a negative photo-resist 8. Light 9 is shone through substrate 1 so that electrodes 2 and 3 form an exposure mark and an image 10 is formed in the photo-resist. The unexposed photo-resist is dissolved away and the uncovered parts of layer 7 are etched away so that the remaining gold layer forms a gate electrode complementary in shape to the source and drain electrodes as indicated by broken lines in Fig. 3. The gate electrode may be deposited first on the substrate and used as a mask for the production of the source and drain electrodes. In a second embodiment an aluminium gate electrode is deposited on a glass substrate and insulated by covering with silicon oxide or by anodizing it. The semi-conductor layer is then deposited and covered with a positive photo-resist which is exposed and developed as before. A layer of tin, silver, gold or antimony is then deposited over the surface of the semiconductor layer and the remaining unexposed photo-resist. The photo-resist is then exposed from above and dissolved thus removing the parts of the metal layer covering it to leave the source and drain electrodes. The source and drain may be deposited first and used as a mask for the gate. In a further embodiment the gate is deposited and covered with silicon oxide and the source and drain electrodes formed on top, by either of the methods previously described. The semiconductor layer which may be CdS is then deposited on top of the electrodes. In the first embodiment a negative photoresist containing finely divided electrode material may be used to produce the electrode. Alternatively a photo-sensitive material may be used which forms metallic particles when it is exposed. If there is a substantialdifference in reflectivity between the deposited electrodes and the substrate light may be passed through the photo-resist and reflected back from the electrodes or substrate to provide an intensity great enough to expose the photo-resist. Either the source or the drain may be produced on the same side of the semi-conductor layer as the gate with the other electrode on the opposite side of the layer. More than one transistor may be simultaneously produced on the same substrate and other circuit elements may also be included. The semi-conductor material may also be In 2 O 3  or ZnCdS, the substrate may be of high-resistivity semi-conductor material, and the gate may be comb-shaped with the source and drain in the form of a plurality of strips or the electrodes may have a concentric configuration.